Electronic balance

ABSTRACT

Provided is a balance with a windshield having a door to be smoothly opened and closed either manually or automatically. Provided is an electronic balance with a windshield including a balance main body including a weighing mechanism connected to a weighing pan, a windshield having doors capable of opening and closing by sliding, and configured to form a weighing chamber by covering the weighing pan, and actuators configured to open and close the doors, wherein the actuator includes a double-acting type air cylinder having two ports serving as air intake ports, an air pump-to be connected to the two ports, two valves respectively interposed between the air pump and the two ports and configured to make the ports communicate with and shut off from the atmosphere, and a control device configured to control the two valves-to make the two ports communicate with the atmosphere when the air pump is stopped. Without a special mechanism, switching between automatic opening and closing and manual opening and closing can be made, and in either automatic or manual opening and closing, the doors of the windshield are smoothly opened and closed.

TECHNICAL FIELD

The present invention relates to an electronic balance with a windshieldhaving a door that can be smoothly opened and closed eitherautomatically or manually.

BACKGROUND ART

Conventionally, as a mechanism to automatically open and close a door ofa windshield, various mechanisms such as a rack-and-pinion and a pulleybelt, etc., as described in Patent Literature 1, etc. are proposed.

CITATION LIST Patent Literature

[Patent Literature 1] Japanese Published Unexamined Utility ModelApplication No. H05-62825

SUMMARY OF INVENTION Technical Problem

However, there is a problem in which when the automatic opening andclosing door is manually opened or closed, it feels very heavy, ormanual opening and closing are impossible. In a configuration in which adoor is opened and closed by means of a rack-and-pinion mechanism, sincethe rack and pinion always mesh with each other, in the case of a manualoperation, the door fells very heavy, and in an attempt to forcibly openthe door, pinion teeth may be damaged. Similarly, also in a mechanismusing a rubber belt such as a pulley belt, the rubber belt and the doorare always in contact with each other, so that the door feels heavy whenit is manually moved.

The present invention was made in view of the above-describedcircumstances, and provides a balance with a windshield having a doorthat can be smoothly opened and closed either automatically or manually.

Solution to Problem

In order to solve the problem described above, an electronic balance ofthe present invention includes a balance main body including a weighingmechanism connected to a weighing pan, a windshield having a doorcapable of opening and closing by sliding, and configured to form aweighing chamber by covering the weighing pan, and an actuatorconfigured to open and close the door, wherein the actuator includes adouble-acting type air cylinder having two ports serving as air intakeports, an air pump to be connected to the two ports, two valvesrespectively interposed between the air pump and the two ports andconfigured to make the ports communicate with and shut off from theatmosphere, and a control device configured to control the two valves tomake the two ports communicate with the atmosphere when the air pump isstopped. With this configuration, in the air cylinder serving as a drivesource of the door, the ports of the air cylinder are made tocommunicate with the atmosphere after the door is automatically openedor closed, so that opening and closing are immediately enabled manuallyas well. Without needing a special switching mechanism, manual openingand closing are also enabled in a state where no load is applied by thedrive source, and the door can be smoothly opened and closed eitherautomatically or manually.

In an embodiment, the electronic balance further includes a pressuresensor configured to monitor a pressure of air discharged from the airpump, wherein the control device is configured to perform control so asto stop the air pump and make the two ports communicate with theatmosphere when the pressure sensor detects a rapid increase in airpressure. Opening and closing operations are performed according tomonitoring of the air pressure, so that finger pinching can beprevented, and high safety is obtained.

In an embodiment, the electronic balance further includes a pressuresensor configured to monitor a pressure of air discharged from the airpump, wherein the control device is configured to control the twovalves, in a case where the pressure sensor does not detect a decreasein air pressure within a predetermined time when the air pump isactivated with one of the two ports being made to communicate with theatmosphere and the other one port being made to shut off from theatmosphere, so as to reverse the communication with the atmosphere andcommunication shut-off from the atmosphere of the two ports. With thisconfiguration, operations in cases of an erroneous operation andhalf-opening are secured.

In an embodiment, a power chamber partitioned and separated from theweighing chamber is formed in the windshield, and the air pump and thetwo valves are disposed inside the power chamber. Vibration of the powerchamber is prevented from being transmitted to the weighing chamber, andthis contributes to reduction of weighing errors.

In an embodiment, the door is hung and supported from an upper portion,and the air cylinder is disposed above the door and connected to a doorhanging portion of the door. The hung and supported door is directlyslid by the air cylinder, so that force transmissibility from the drivesource is high, and the door can be smoothly opened and closed.

In an embodiment, the control device is configured to control the valvesso that communication of the two ports with the atmosphere is shut offduring calibration of the balance main body. During calibration, thedoor is locked so as not to move, and the door is prevented from beingopened by mistake and harmfully influencing the calibration.

In an embodiment, the control device is configured to control the valvesso that communication and shutting-off between the two ports and theatmosphere are switched according to a command input. Without providinga special switching mechanism, switching between automatic opening andclosing and manual opening and closing of the door can be made only bycontrol of the valves, and this switching can be made only by a commandinput, and this is very convenient for use.

Effect of Invention

With the configuration described above, a balance with a windshield canbe provided including a door that is capable of being smoothly openedand closed either automatically or manually.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electronic balance with a windshieldaccording to a first embodiment.

FIG. 2 is a plan view of an engagement member.

FIG. 3 is a bottom view of the engagement member.

FIG. 4 is a right side view of the engagement member.

FIG. 5 is a perspective view of the engagement member.

FIG. 6 is a perspective view of a flat plate.

FIG. 7 is an enlarged view of portion A in FIG. 1 in a state where theengagement member is pulled out.

FIG. 8 is a sectional view taken along line VIII-VIII in FIG. 7.

FIG. 9 are views illustrating an engaged state of the engagement memberand an engagement hole.

FIG. 10 are conceptual diagrams illustrating an engaged state of a floormember and the engagement member.

FIG. 11 is a top view of a cylinder box in a state where a cover isremoved.

FIG. 12 is a right side view of the windshield in the state where thecover is removed.

FIG. 13 is a sectional view taken along line XIII-XIII in FIG. 11.

FIG. 14 is an explanatory view to describe a structure of a door 11.

FIG. 15 is a block diagram of a door opening and closing mechanismaccording to the first embodiment.

FIG. 16 is an operation chart of the door opening and closing mechanismaccording to the first embodiment.

FIG. 17 is a flowchart of door opening and closing operations accordingto the first embodiment.

FIG. 18 is a perspective view of an electronic balance with a windshieldaccording to a second embodiment.

FIG. 19 is a block diagram of a door opening and closing mechanismaccording to the second embodiment.

FIG. 20 is an operation chart of the door opening and closing mechanismaccording to the second embodiment.

FIG. 21 is a block diagram of a door opening and closing mechanismaccording to a third embodiment.

FIG. 22 is an operation chart of the door opening and closing mechanismaccording to the third embodiment.

FIG. 23 is an example of a modification.

FIG. 24 is an example of a modification.

DESCRIPTION OF EMBODIMENTS Configuration of Electronic Balance withWindshield

Hereinafter, preferred embodiments relating to a configuration of thepresent disclosure are described with reference to the drawings. FIG. 1is a perspective view of an electronic balance 1 with a windshieldaccording to a first embodiment.

As illustrated in FIG. 1, the electronic balance 1 with a windshieldincludes a balance main body 30, a windshield 10 to be attached to thebalance main body 30, a connector 8 that connects the balance main body30 and the windshield 10, and a control panel 35.

The balance main body 30 includes, on an upper surface thereof, aweighing pan 31 on which a specimen is placed. A control unit 34 thatcontrols a weighing mechanism connected to the weighing pan 31 and thewindshield 10 is disposed inside the balance main body 30. Onto theupper surface of the balance main body 30, a floor member 32 is fixed, adust plate 29 is placed on an upper surface of the floor member 32, andfurther, a ring-shaped windshield ring 28 is placed on the dust plate29. The dust plate 29 prevents a specimen spilling out of the weighingpan 31 from falling on the balance main body 30, and the windshield ring28 plays a role in preventing wind effects on the weighing pan 31.

The windshield 10 is disposed on the upper surface of the balance mainbody 30 so as to enclose a periphery of the weighing pan 31, andprevents air flow during weighing, for example, wind from an airconditioner, breath of a person at the time of weighing, and an air flowgenerated when a person walks, etc., from acting as a wind pressure on aload-applied portion centered on the weighing pan 31 and influencingweighing.

The windshield 10 has a bottomless box shape, and has a front glass 12at a front surface, a box-shaped case 18 at a back portion, doors 11 atportions of left and right side walls, and an upper surface door 13 atthe upper surface, and as a space defined by these, a weighing chamber 6having a rectangular parallelepiped shape is formed inside.

The doors 11 can respectively move forward and rearward along rails 14 aprovided on a frame 14 as a frame member at a lower portion of thewindshield 10, and the door 11 can move forward and rearward along rails20 a provided in cylinder boxes 20 as frame members at an upper portionof the windshield 10. The front glass 12 is fixed to the front sides ofthe frame 14 and the cylinder boxes 20 by fixing members such as bolts.

The front glass 12, the upper surface door 13, and the left and rightdoors 11 are made of transparent glass or resin so that an internalstate can be observed. To each of the upper surface door 13 and thedoors 11, a handle 15 that assists sliding is attached.

The cylinder boxes 20 are provided to form the left and right uppersides of the windshield 10 having a substantially rectangularparallelepiped shape. In the cylinder box 20, an air cylinder 40 that isa means for opening and closing the door 11 is housed. Inside the case18, a power chamber 17 is formed.

The control panel 35 is for operating the balance main body 30 and thewindshield 10, and is provided separately from the balance main body 30.This is to prevent vibration caused by an operation such as pushing on aswitch from influencing weighing. The control panel is separated fromthe balance main body, so that a user can freely arrange the controlpanel at a position easy to operate. The control panel 35 is connectedto the balance main body 30 by a cable 39. The control panel 35 and thebalance main body 30 may be connected by wireless communication.

The control panel 35 includes, on an upper surface thereof, a displayunit 38 to display weighing results and states, switches 37 foroperation, and an infrared sensor 36. The infrared sensor 36 is anopening and closing switch of the doors 11, and only by holding a handover the infrared sensor, can the doors 11 be automatically opened andclosed. A press switch may be provided in place of the infrared sensor36, and a configuration in which both of a press switch and the infraredsensor 36 are provided is also preferable. To the infrared sensor 36, abalance operating function other than the door 11 opening and closingfunction may be assigned. It is also possible that two left and rightinfrared sensors 36 are provided and configured to respectively open andclose corresponding doors 11.

The windshield 10 and the balance main body 30 are connected by theconnector 8. The windshield 10 receives electric power and commandsignals from the balance main body 30 through the connector 8.

Attaching and Detaching Mechanism

In the frame 14, a pair of left and right attaching and detachingmechanisms 70 are provided. The attaching and detaching mechanisms 70are described in detail. In the frame 14, an engagement hole 19 isformed that penetrates through the frame to the inside, and in theengagement hole 19, an engagement member 72 is inserted. The engagementmember 72 is inserted through the engagement hole 19 and engaged with ordisengaged from the floor member 32 fixed to a bottom surface of thebalance main body 30, and accordingly, the windshield 10 is attached toor detached from the balance main body 30.

The engagement member 72 includes a flat plate 73 and a housing 74. FIG.2 is a plan view of the engagement member 72, FIG. 3 is a bottom view ofthe engagement member 72, FIG. 4 is a right side view of the engagementmember 72, FIG. 5 is a perspective view of the engagement member 72, andFIG. 6 is a perspective view of the flat plate 73.

The flat plate 73 is attached to the housing 74, and directly engageswith the floor member 32 fixed to the balance main body 30. The flatplate 73 is made of a material with high strength such as a metal plate.The flat plate 73 is fixed to the housing 74 by a fixation means such asa machine screw 76 in a state where a contact portion 73 a, which is thetip end portion, protrudes. The contact portion 73 a is a portion thatcomes into contact with the floor member 32 of the balance main body 30,and is formed to be wider than other portions to increase the contactarea.

In the housing 74, an end portion at the side opposite the end portionat the side from which the contact portion 73 a protrudes is a gripportion 74 a to be gripped at the time of an operation of inserting andpulling out the engagement member 72.

At upper portions of side wall portions 74 b of the housing 74, eavesportions 74 c overhanging to the outer sides of the side wall portions74 b are formed.

Holes are formed so as to become orthogonal to the side wall portions 74b of the housing 74, and inside the holes, a pair of left and right lockpins 75 are disposed. Both of the lock pins 75 are energized so as toprotrude to the outer sides of the side wall portions 74 b (the arrowdirections in FIG. 2) by an elastic body such as a coil spring (notillustrated) interposed between the lock pins 75.

Next, the engagement holes 19 provided in the frame 14 are described.FIG. 7 is an enlarged view of portion A in FIG. 1, and illustrates astate where the engagement member 72 is pulled out from the engagementhole 19. FIG. 8 is a sectional view taken along line VIII-VIII in FIG.7.

At two positions opposed to each other on the left and right wallportions of the frame 14, the engagement holes 19 are formed. Theengagement holes 19 are orthogonal to the side walls of the frame 14,and are formed to penetrate through the frame 14. The engagement holes19 are guide holes to guide advancing/retreating movements of theengagement members 72.

A front surface shape of the engagement hole 19 is a substantially Ishape consisting of an upper horizontal portion 19 a, a lower horizontalportion 19 c, and a vertical portion 19 b connecting both horizontalportions. The engagement hole 19 is configured so that the eavesportions 74 c of the housing 74 are fitted into the upper horizontalportion 19 a, the side wall portions 74 b of the housing 74 arepositioned at the vertical portion 19 b, and the flat plate 73 isinserted through the lower horizontal portion 19 c. Accordingly, theengagement member 72 is smoothly inserted and pulled out along theengagement hole 19 without slipping out of the engagement hole 19.

In the vertical portion 19 b of the engagement hole 19, locking recessportions (19 d and 19 e) are formed at two positions in the depthdirection. The locking recess portions (19 d and 19 e) are formed at adeepness at which they engage with the lock pin 75, and when theengagement member 72 is inserted in and pulled out from the engagementhole 19, the lock pins 75 of the engagement member 72 engage with eitherthe locking recess portion 19 d or 19 e. Accordingly, the engagementmember 72 is stopped and fixed at a predetermined position in theengagement hole 19.

Subsequently, the floor member 32 of the balance main body 30 with whichthe windshield 10 directly engages is described with reference toFIG. 1. The floor member 32 itself is a component conventionallyattached to the balance main body 30.

In the upper surface of the balance main body 30, a through hole (notillustrated) is provided. This through hole communicates with the insideof the balance main body 30, and makes the air pressure inside thebalance main body 30 and the air pressure around the balance main body30 equal to each other, and prevents weighing errors caused by an airpressure change. To prevent dust from entering from the through holewhile making the through hole and the atmosphere communicate with eachother, the floor member 32 is attached to the upper surface of thebalance main body 30 in a state where the floor member is separated fromthe balance main body 30 by a spacer 33.

The floor member 32 is disposed to be centered at the weighing pan 31,and is fixed to the upper surface of the balance main body 30 by machinescrews or the like. The floor member 32 is normally made of stainlesssteel, or a chromed steel material, etc. A casing constituting thebalance main body 30 is formed of an aluminum die-casting or syntheticresin molding product, but if the weighing pan 31 is directly disposedon this casing, it becomes difficult to remove a specimen that fell ontothe casing surface. Further, in the case where the casing is made ofsynthetic resin, depending on the kind of specimen, a situation in whichthe casing itself is dissolved by the specimen is assumed to occur. Bydisposing the floor member 32, even if a specimen such as a liquid orpowder falls, the floor member 32 is highly resistant to the specimen,and the surface of the floor member is machined to be flat and smooth bymirror-like finishing, so that the specimen can be easily wiped off. Inaddition, the material forming the floor member is a metal plate, sothat its original physical strength is also extremely high. In thepresent embodiment, by locking the engagement members 72 to this floormember 32, the windshield 10 is fixed to the balance main body 30.

FIG. 9 are views each illustrating a fitting-through state of theengagement member 72 and the engagement hole 19, and illustrateperspective views of the frame 14 from the inside of the windshield 10.FIGS. 10 are conceptual diagrams illustrating an engagement statebetween the floor member 32 and the engagement member 72.

FIGS. 9(A) and 10(A) illustrate a state where the engagement member 72is disengaged from the engagement hole 19.

FIGS. 9(B) and 10(B) illustrate a state where the engagement member 72is inserted in the engagement hole 19, and the lock pins 75 arepositioned at the locking recess portions 19 e recessed in theengagement hole 19. The lock pins 75 are energized so as to protrudeoutside by the coil spring not illustrated, and engage with the lockingrecess portions 19 d (or 19 e) and fix the engagement member 72 at theposition of the locking recess portions. In this state, the contactportion 73 a of the flat plate 73 is not in engagement with the floormember 32, and the windshield 10 is detachable from the balance mainbody 30.

FIGS. 9(C) and 10(C) illustrate a state where the engagement member 72is further inserted in the engagement hole 19, and the lock pins 75 arepositioned at the locking recess portions 19 d. The lock pins 75 engagewith the locking recess portions 19 d and fix the engagement member 72in a state where the tip end of the flat plate 73 protrudes to theinside of the windshield 10. Accordingly, the contact portion 73 a ofthe flat plate 73 closely engages with a back surface of the floormember 32, and by this engagement, the windshield 10 is firmly fixed tothe balance main body 30.

Operation and Effect of Attachment and Detachment

In the present embodiment, the windshield 10 has a door 11 automaticopening and closing function, however, a drive source and a drivemechanism for automatic opening and closing are all housed inside thewindshield 10 in a form that does not influence weighing (described indetail later). The attaching and detaching mechanism 70 fixes thewindshield 10 by using the floor member 32 conventionally provided, sothat without making any modification to the balance main body 30 side,the windshield 10 can be fixed. Conventionally, a windshield with a dooropening and closing function has a problem in which the degree offreedom of design is low because the balance and the windshield areconfigured and designed as an integrated body. In the presentembodiment, the balance and the windshield are configured as separatebodies independent from each other, and the balance main body 30 and thewindshield 10 can be designed separately, so that the degree of freedomof design is high. The balance main body 30 can be freely designedwithout restrictions in design caused by the windshield 10 and theaddition of the door automatic opening and closing function.

A balance with a windshield having an automatic opening and closingfunction is expensive, however, when either the windshield or thebalance main body malfunctioned, both of these became unusable, and thiswas uneconomical. In the present embodiment, a malfunctioning one can beimmediately replaced with a new one, and this is economical. Also duringrepair, the other that is not malfunctioning can be continuously used.

Further, the windshield 10 is fixed by using the floor member 32conventionally provided, so that if the conditions such as dimensionsare met, the windshield 10 having the door automatic opening and closingfunction can be fitted to an existing electronic balance, and inaddition, the windshield 10 can be firmly fixed and used, and this ishighly convenient. Although the windshield 10 is freely attachable anddetachable, the windshield 10 and the balance main body 30 can be firmlyheld and integrated, and are easy to carry around, and no troublesomeassembling operations are required.

When the electronic balance 1 with a windshield is disposed inside aglovebox the opening of which is narrow, the electronic balance 1 with awindshield can be disassembled into the balance main body 30 and thewindshield 10, and these can be put into the glovebox separately, andfurther, they can be easily assembled inside the glovebox.

Door Structure

The cylinder box 20 has a cover 20 b covering the upper surface and theside surfaces of the cylinder box. FIG. 11 is a plan view of thecylinder box 20 in a state where the cover 20 b is removed, and is anexplanatory view to describe the inside of the cylinder box 20. FIG. 12is a right side view of the windshield 10 in the state where the cover20 b is removed. FIG. 13 is a sectional view taken along line XIII-XIIIin FIG. 11, and is an explanatory view to illustrate the shape andoperation of a holder 16. FIG. 14 is a perspective view of the cylinderbox 20 and the door 11, and is an explanatory view to describe thestructures of these.

Inside the cylinder box 20, the air cylinder 40 is fixed. The aircylinder 40 is a double-acting type, and both of the forward andbackward strokes of reciprocating motion of a piston 41 inside the aircylinder 40 are made by air pressure. Therefore, ports to feed air tothe inside of the air cylinder 40 are provided at two positions. At thefront side of the cylinder tube 42 having the piston 41 inside, aretreat-side port 46 for making the piston 41 move rearward by fed airis provided. In the same manner, at the rear side of the cylinder tube42, an advance-side port 44 for sending the piston 41 forward isprovided.

Air tubes 47 connected to the respective ports pass through a hole 20 cprovided in a bottom surface 20 f of the cylinder box 20 and connect tothe power chamber 17 inside the case 18. In the power chamber 17, pumpsserving as drive sources of the air cylinder 40 and solenoid valves tocontrol the flow and stoppage of air are housed.

The power chamber 17 is formed by being separated from the weighingchamber 6 so as not to influence weighing with vibration, etc. Airintake and exhaust ports (not illustrated) formed in the power chamber17 are directed in a direction opposite to the weighing chamber 6 sothat air intake and exhaust do not influence weighing.

Conventionally, when for example, a rack-and-pinion or a rubber pulleyis selected as a drive mechanism, a motor serving as a drive source isdisposed close to the door from the viewpoint of transmissionefficiency. However, in this case, vibration of the motor serving as adrive source is transmitted to the weighing chamber, so that there isconcern that the vibration influences weighing. By selecting an aircylinder as a drive mechanism, it becomes unnecessary to dispose the airpump as a power source close to the door, and the air pump can bedisposed at a free place. By providing the power chamber 17 in which theair pump is housed by separating to be away from the weighing chamber 6,influences of vibration of the power source on weighing can be reduced.

The cylinder box 20 is formed to be hollow, and inside this, the aircylinder 40 is disposed parallel to the door 11 and fixed while beingseparated from the bottom surface 20 f of the cylinder box 20. The aircylinder 40 is disposed inside the cylinder box 20, and this preventsdust entrance and transmission of air vibration from the air cylinder 40to the weighing chamber 6.

At front and rear end portions of the door 11, holders 16 are disposed.The door 11 is vertically sandwiched by two U-shaped clamp portions 16 aformed at upper and lower portions of the holder 16, and held by beingwrapped by the holder 16 consisting of a combination of the clampingportions 16 a and a side surface portion 16 b connecting the upper andlower clamping portions 16 a. If the door 11 is simply clamped and hungdown from above, there is a risk that the door 11 may fall off, however,since the door 11 is firmly held by the holder 16 by being wrapped bythe holder 16, there is no risk of falling off.

In the bottom surface of the cylinder box 20, a guide hole 20 d isformed in a front-rear direction that is a sliding direction of the door11. At a portion higher than the upper clamping portion 16 a, a flangeportion 16 c is formed orthogonally to the door 11 (guide hole 20 d).The flange portion 16 c protruding leftward and rightward engages inthis guide hole 20 d and supports the door 11 in a hanging manner.Accordingly, the door 11 is disposed in a non-contact manner t with therail 14 a formed on the frame 14, and held slidably along the guide hole20 d. When dust and sand, etc., enter the rail 14 a, a problem occurs inwhich the sliding resistance when the door 11 opens or closes increasesand it becomes difficult to open and close the door, however, thisproblem is prevented by hanging the door 11 itself from the upperportion.

In the holder 16 disposed at the front end of the door 11, a couplingportion 16 d is formed on an upper surface of the flange portion 16 c.At the center of the coupling portion 16 d, a coupling hole 16 e isformed along the door opening and closing direction, and the tip end ofa piston rod 43 extending from the piston 41 of the air cylinder 40 isfitted in this coupling hole 16 e and fixed. By the piston 41 (pistonrod 43) connected to the door 11 through the holder 16 and by the piston41 moving forward and rearward by air, the holder 16 slides along theguide hole 20 d and the door 11 opens and closes. The air cylinder 40 isfixed while being separated from the bottom surface inside the cylinderbox 20, so that the air cylinder does not obstruct movements of the door11.

Operation and Effect of Door Structure

The air cylinder 40 serving as a drive source of the door 11 is disposedsubstantially right above the door 11 and parallel to the slidingdirection of the door 11. The holders 16 that support the door in ahanging manner support the door 11 by lower portions, and are connectedat upper portions to the air cylinder 40, and the air cylinder 40 opensand closes the door 11 by directly sliding the holders 16 that supportsthe door 11 in a hanging manner The holder 16 on which the door is hung,specifically, the flange portion 16 c that serves as a sliding portionwhen opening and closing the door 11 is disposed close to the aircylinder 40 serving as a drive mechanism. Further, only front and rearend portions of the door 11 are hung with the holders 16, and a slidingarea when the door 11 opens and closes is small, and sliding resistancewhen the door 11 opens and closes is also small. In the presentembodiment, the holders 16 and the cylinder boxes 20, and in addition,the doors 11 are also made of resin, so that they are light in weightand have small sliding resistance. With this configuration, forcetransmissibility from the air cylinder is high, the door 11 can beopened and closed with small force, and the door 11 can be smoothlyopened and closed.

When the door of the windshield is opened and closed by using aconventional opening and closing mechanism, for example, a rubberpulley, in order to transmit power of the motor to the door having acertain degree of weight, the pulley at the door portion must be madelarge or the power of the motor must be made high. The balance is easilyinfluenced by wind, and wind is easily produced by high-speed openingand closing of the door, so that in order also to decrease the openingand closing speed, the pulley must be made large for decreasing thespeed. If the door is formed to be thin and light in weight, it isdifficult to transmit power to the door and the motor is inevitably madelarge. Further, the motor needs to be disposed near (substantially, atthe upper portion of) the door, and this disposition of a large-sizedmotor is awkward, and makes the appearance unsightly. By disposing theair cylinder 40 long in one direction along the door 11 at the upperportion of the door 11, the windshield 10 can be formed into asubstantially rectangular parallelepiped shape, and the appearance andconfiguration become simple.

Block Diagram

FIG. 15 is a block diagram illustrating an opening and closing mechanism60 of the left or right door 11 of the electronic balance 1 with awindshield. The opening and closing mechanism 60 is a mechanism to openand close the left or right door 11, and another set of the componentsillustrated in FIG. 15 is present, and the components are the same, sothat they are omitted in illustration. In the present embodiment, a pumpto move forward (advance) the piston 41 of the air cylinder 40 and apump to move rearward (retreat) the piston 41 are present separately.

Both of a first pressurization pump 62A and a second pressurization pump62B are air pumps. These pumps are drive sources of the air cylinder 40,and compress air and feed the compressed air to the air cylinder 40, andmove the piston 41 by air pressures to open and close the door 11.

Outlet sides of a first one-way solenoid valve 66A and a second one-waysolenoid valve 66B are opened to the atmosphere, and by opening andclosing the valves, the flow and stoppage of air are controlled.

A first pressure sensor 64A monitors a pressure of air discharged fromthe first pressurization pump 62A, and a second pressure sensor 64Bmonitors a pressure of air discharged from the second pressurizationpump 62B.

To the advance-side port 44 provided at the rear side of the aircylinder 40, the first pressurization pump 62A is connected. Thisconnection has a branch halfway, and the first pressure sensor 64A andthe first one-way solenoid valve 66A are further connected. To theretreat-side port 46 provided at the front side of the air cylinder 40,the second pressurization pump 62B is connected. This connection has abranch halfway, and the second pressure sensor 64B and the secondone-way solenoid valve 66B are connected to this branch. Thesecomponents are connected by the air tubes 47, respectively.

Operations of the respective components of the opening and closingmechanism 60 are controlled by the control unit 34 of the balance mainbody 30. For this reason, an instruction for the opening and closingmechanism 60 is performed through the balance main body 30, however, aconfiguration is also preferable in which a windshield control unit tocontrol the windshield 10 is provided inside the windshield 10, and acommand input is directly transmitted from the control panel 35 to thewindshield control unit. In this case, a configuration is alsopreferable that a command input unit is provided in the windshield 10itself so that the windshield 10 can be operated alone.

Operation When Opening and Closing Door

Next, operations of the respective components when the door 11 isautomatically opened and closed are described. FIG. 16 is an operationchart of the opening and closing mechanism 60.

First, in a “standard state” in which a user can manually open and closethe door 11, neither of the first pressurization pump 62A and the secondpressurization pump 62B is activated, and the first one-way solenoidvalve 66A and the second one-way solenoid valve 66B are open. Becauseneither of the pressurization pumps (62A and 62B) operates, and both ofthe one-way solenoid valves (66A and 66B) are opened and communicatewith the atmosphere, so that no load is applied from the air cylinder40, and the door 11 can be smoothly manually opened and closed.

When a command to “open/close door” is input from the infrared sensor 36of the control panel 35, the control unit 34 commands the respectivecomponents to operate.

In a case of an “automatic opening operation” to open the door 11, thatis, in a case where the piston 41 of the air cylinder 40 is movedrearward, the second one-way solenoid valve 66B is closed, andpressurization of the second pressurization pump 62B is started. At thistime, the first pressurization pump 62A is not activated, and the firstone-way solenoid valve 66A is open, so that the piston 41 is movedrearward by an air pressure, and the door 11 is opened.

When the door 11 fully opens, the air pressure rapidly increases, sothat when this change is detected by the second pressure sensor 64B, thesecond pressurization pump 62B is stopped, the second one-way solenoidvalve 66B is opened, and the compressed air inside the air cylinder isreleased to the atmosphere, and the mechanism returns to the standardstate.

In a case of an “automatic closing operation” to close the door 11, thatis, in a case where the piston 41 of the air cylinder 40 is movedforward, the first one-way solenoid valve 66A is closed, andpressurization of the first pressurization pump 62A is started. At thistime, the second pressurization pump 62B does not operate, and thesecond one-way solenoid valve 66B is open, so that the piston 41 ismoved forward by an air pressure, and the door 11 is closed.

When the door 11 fully closes, the air pressure rapidly increases again,so that when this change is detected by the first pressure sensor 64A,the first pressurization pump 62A is stopped, the first one-way solenoidvalve 66A is opened, and the compressed air inside the air cylinder isreleased to the atmosphere, and the mechanism returns to the standardstate.

On the other hand, when calibration is performed, the first one-waysolenoid valve 66A and the second one-way solenoid valve 66B are closed.Both of the one-way solenoid valves (66A and 66B) are closed, the piston41 can move neither forward nor rearward, and the door 11 is locked.This is to prevent the door from being unexpectedly opened duringcalibration operation and influencing calibration. After the calibrationis finished, the first one-way solenoid valve 66A and the second one-waysolenoid valve 66B are opened, and the mechanism returns to the standardstate.

In this way, the door 11 is automatically locked during calibrationoperation. The door 11 may be configured to be locked according to acommand from the switch 37. Not only during calibration, the door 11 canalso be locked during transportation.

Flowchart

Next, a flow of opening and closing operations of the door 11 isdescribed with reference to the flowchart in FIG. 17.

In Step S101, from the infrared sensor 36 of the control panel 35, whichis a switch to open and close the door 11, a command signal toopen/close the door 11 is input. When the signal is not input, themechanism waits until the signal is input.

When a command is input, the process shifts to Step S102, and whetherthe door position is at a closed position or an open position ischecked. In the present embodiment, the control unit 34 keeps a lastopening/closing operation of the door 11 in memory, and makesdetermination according to the content. A configuration is also possiblein which a position sensor is provided to check the position of the door11.

First, a case where the door 11 is at the closed position (Steps S103 toS108) is described.

The process shifts to Step S103, and in order to open the door 11 thatis at the closed position, the “automatic opening operation” for thedoor 11 is performed. In detail, the second one-way solenoid valve 66Bis closed, and operation of the second pressurization pump 62B isstarted. At this time, the first one-way solenoid valve 66A is leftopen, and the first pressurization pump 62A is not activated (refer toFIGS. 15 and 16).

Next, the process shifts to Step S104, and whether the door 11 hasstarted to move is checked. When the door 11 starts to move, the airpressure rapidly decreases, so that when a value of the second pressuresensor 64B rapidly decreases within a predetermined time, for example,within one second, it is determined that the door 11 has started anopening operation. When the door 11 does not start to move within thepredetermined time, the control unit 34 determines that “door 11 hasalready been opened,” and the process shifts to Step S109, and then, the“automatic closing operation” is started (described later).Alternatively, when a value of the second pressure sensor 64B exceeds apredetermined value, it is also possible to determine that the door hasnot started to move. A last position of the door 11 is kept in memory,however, in the present embodiment, manual opening and closing are alsopossible, and the position of the door 11 is moved by a user in somecases. Against such a case or an erroneous determination of the door 11position, security is provided by this Step S104.

When movement of the door 11 is started, the process shifts to StepS105, and whether the opening operation of the door 11 has been finishedis checked. When the movement of the door 11 is completed, the airpressure increases again, and when a value of the second pressure sensor64B increases again within a predetermined time, it is determined thatthe opening operation of the door 11 has been finished. When the valueof the second pressure sensor 64B does not increase within thepredetermined time, air leakage or malfunction is suspected, so that toperform error handling, the process shifts to Step S106.

In Step S106, as the error handling, a warning tone is produced, anerror is displayed on the display unit 38, the operation of the secondpressurization pump 62B is stopped, the second one-way solenoid valve66B is opened, and the mechanism is brought to an emergency stop.

When completion of the opening operation of the door 11 is confirmedaccording to an air pressure increase, the process shifts to Step S107,the operation of the second pressurization pump 62B is stopped, thesecond one-way solenoid valve 66B is opened, and the automatic operationis normally finished.

Last, the process shifts to Step S108, the mechanism returns to thestandard state, and manual opening and closing are enabled.

Next, a case (S109 to S113) where the door 11 is at the open position inStep S102 is described.

The process shifts to Step S109, and in order to close the door 11 thatis at the open position, the “automatic closing operation” of the door11 is performed. In detail, the first one-way solenoid valve 66A isclosed, and operation of the first pressurization pump 62A is started.At this time, the second one-way solenoid valve 66B is left open, andthe second pressurization pump 62B is not activated (refer to FIGS. 15and 16).

Next, the process shifts to Step S110, and whether the door 11 hasstarted to move is checked. As in Step S104, when a value of the firstpressure sensor 64A rapidly decreases within a predetermined time, it isdetermined that the door 11 has started a closing operation. When thedoor 11 does not start to move within the predetermined time, thecontrol unit 34 determines that “the door 11 has already been closed,”and the process shifts to Step S103, and then, the “automatic openingoperation” is started. Like Step S104, this step S110 also providessecurity against a case where the door 11 position is moved by manualopening and closing and an erroneous determination.

When movement of the door 11 is started, the process shifts to StepS111, and whether the closing operation of the door 11 has been finishedis checked. Completion of the movement of the door 11 is determined whenthe value of the first pressure sensor 64A increases again within apredetermined time. When the value of the first pressure sensor 64A doesnot increase within the predetermined time, to perform error handlingagain, the process shifts to Step S112. When completion of the doorclosing operation is confirmed according to an increase in value of thefirst pressure sensor 64A within the predetermined time, the processshifts to Step S113.

In Step S112, as error handling, a warning tone is produced, an error isdisplayed on the display unit 38, the operation of the firstpressurization pump 62A is stopped, the first one-way solenoid valve 66Ais opened, and the mechanism is brought to an emergency stop.

When an increase in value of the first pressure sensor 64A within thepredetermined time is confirmed, the process shifts to Step S113, theoperation of the first pressurization pump 62A is stopped, and the firstone-way solenoid valve 66A is opened.

Last, the process shifts to step S108, the mechanism returns to thestandard state, and manual opening and closing are enabled.

Step S111 and Step S105 double as a safety function to prevent fingerpinching, etc. When the door 11 is about to be automatically closed oropened, even if one of the operator's fingers is pinched in the door 11,a specimen or the like is caught in the door 11, or trouble occurs inthe movement of the door 11 and the movement is forcibly stopped, theair pressure increases, so that this air pressure increase is detectedby the first pressure sensor 64A (or the second pressure sensor 64B),and the operation of the door 11 is immediately stopped, both of theone-way solenoid valves (66A and 66B) are made to communicate with theatmosphere, and the load on the door 11 is eliminated, and safety issecured.

Effect of Release to Atmosphere

When one pressurization pump operates, the other pressurization pumpdoes not operate, and only one solenoid valve is closed, and the othersolenoid valve is opened and communicates with the atmosphere. When thepump that has been operating stops, the closed solenoid valve opens andcommunicates with the atmosphere. In other words, all of the one-waysolenoid valves are configured to open and communicate with theatmosphere when the pressurization pumps stop. After the door 11 isautomatically opened/closed, air is released to the atmosphere, and theload on the door 11 is eliminated, and it becomes possible to smoothlymanually move the door 11. The door 11 is automatically openable andclosable, however, after it is automatically opened/closed, manualopening and closing are enabled immediately without a special operation.A mechanism to disconnect the drive source and the drive mechanism formanual/automatic switching and an operation therefor itself areunnecessary, so that extremely high usability is obtained.

When the door is opened/closed by using resistance of rubber as in thecase of using a conventional mechanism, for example, a pulley or thelike, a problem occurs in which even when the door is to be manuallyopened, the door is heavy or cannot be opened due to a load (slidingresistance) caused by interlock of the rubber with the drive source. Inthe present embodiment, as a door 11 opening and closing mechanism, anair cylinder is employed, and after finishing opening and closing, allof the valves are opened to communicate with the atmosphere, so that noair pressure is applied and the door can be opened and closed smoothly,and even when the door is manually opened/closed, there is no risk ofbreakage and malfunction.

The door can be manually opened and closed, so that the door 11 can bestopped at an arbitrary position, and the degree of freedom in use ishigh. Even when the door 11 is at a halfway position, according to aninput of a command from the infrared sensor 36, the door 11 is closed oropened.

Also when the door opening and closing mechanism malfunctions ordegrades with age, the door cannot be opened or closed with aconventional mechanism, however, by using the air cylinder 40, even whena packing to prevent air leakage degrades with age, only the dooropening and closing speed decreases due to the air leakage, and evenwhen malfunction occurs, manual opening and closing are possible, andthis is highly convenient.

When weighing is to be performed by using a space around the balancemain body 30, the windshield 10 can be detached, and when the windshield10 is attached to the balance main body 30, the doors 11 of thewindshield can be opened and closed either automatically or manually, sothat the degree of freedom for use is high.

The mechanism is also configured so that by switching between the“automatic opening operation” and the “automatic closing operation”according to monitoring of the air pressure, opening/closing of thedoors 11 is secured even when an erroneous operation occurs or the door11 is at a halfway position, and the automatic opening operation orautomatic closing operation is stopped when an abnormality occurs, andtherefore, a high degree of safety and a high degree of usability areobtained.

Second Embodiment

FIG. 18 is a perspective view of a balance 101 with a windshieldaccording to a second embodiment. FIG. 19 is a block diagram of anopening and closing mechanism 160 of the balance 101 with a windshieldaccording to the second embodiment.

The balance 101 with a windshield according to the second embodiment isconfigured in common with the electronic balance 1 with a windshieldaccording to the first embodiment except that the balance 101 with awindshield includes an automatic calibration mechanism 80 that performsautomatic calibration inside the balance main body 30 and that theconfiguration of the opening and closing mechanism 160 serving as amechanism to automatically open and close the door is different. Unlikethe opening and closing mechanism 60 of the first embodiment, theopening and closing mechanism 160 of the present embodiment serving as amechanism to open and close the door is provided not independentlybetween the left and the right. Therefore, left and right doors aredescribed as a left door 11A and a right door 11B. Left and right aircylinders for opening and closing these doors are distinguished as aleft air cylinder 40A and a right air cylinder 40B. Each of the aircylinders (40A/40B) includes a retreat-side port (46A/46B) and anadvance-side port (44A/44B) to take in air, and a piston (41A/41B).

As illustrated in FIG. 19, the left air cylinder 40A and the right aircylinder 40B shares one pressurization pump 62C as a drive source. Onepressure sensor 64C monitors the pressure of air discharged from thepressurization pump 62C. Outlet sides of all of five one-way solenoidvalves (66C, 66D, 66E, 66F, and 66G) are opened to the atmosphere.Two-way solenoid valves (68C, 68D, 68E, 68F, and 68G) provided in thepresent embodiment each have two connect ports, and inlet sides are eachconnected to the pressurization pump 62C, and outlet sides are eachconnected to the left air cylinder 40A, the right air cylinder 40B, oran air bag 81 to control the flow and stoppage of air.

To the advance-side port 44A provided at the rear side of the left aircylinder 40A, the first two-way solenoid valve 68C is connected. Thisconnection has a branch halfway, and the first one-way solenoid valve66C is also connected. To the retreat-side port 46A provided at thefront side of the left air cylinder 40A, the second two-way solenoidvalve 68D is connected, and this connection has a branch halfway, andthe second one-way solenoid valve 66D is also connected.

In the right air cylinder 40B, in the same manner as described above, tothe advance-side port 44B provided at the rear side, the third two-waysolenoid valve 68E and the third one-way solenoid valve 66E areconnected, and to the retreat-side port 46B provided at the front side,the fourth two-way solenoid valve 68F and the fourth one-way solenoidvalve 66F are connected.

The automatic calibration mechanism 80 automatically calibrates thebalance 101 with a windshield by loading and unloading a built-in weight82 onto and from the balance by inflation and deflation of the air bag81. Automatic calibration using an air bag is disclosed in detail inJapanese Published Unexamined Patent Application No. 2008-032610. To theair bag 81, the fifth two-way solenoid valve 68G and the fifth one-waysolenoid valve 66G are connected.

FIG. 20 illustrates operations of the respective components to operatethe left door 11A, the right door 11B, and the built-in weight 82 of theautomatic calibration mechanism 80.

As illustrated in FIG. 20, in a “standard state” where the respectivefunctions are not activated at all, the pressurization pump 62C does notoperate, and all of the one-way solenoid valves (66C, 66D, 66E, 66F, and66G) are opened, and all of the two-way solenoid valves (68C, 68D, 68E,68F, and 68G) are closed. In this state, both of the left door 11A andthe right door 11B can be manually opened and closed.

First, automatic opening and closing of the left door 11A are described.In the case of an “automatic opening operation” of the left door 11A,that is, when the piston 41A (and the left door 11A connected to thispiston) is moved rearward, the second one-way solenoid valve 66D isclosed, the second two-way solenoid valve 68D is opened, andpressurization of the pressurization pump 62 is started. At this time,air passes through the opened second two-way solenoid valve 68D, and thepiston 41A is moved rearward by an air pressure, and the left door 11Ais opened.

When the left door 11A fully opens, the air pressure rapidly increases,so that when this change is detected by the pressure sensor 64C, thepressurization pump 62C is stopped, the second two-way solenoid valve68D is closed, the second one-way solenoid valve 66D is opened,compressed air inside the left air cylinder 40A is released to theatmosphere, the pressure inside the left air cylinder 40A decreases tothe atmospheric pressure, and the mechanism returns to the standardstate.

In the case of an “automatic closing operation” of the left door 11A,that is, when the piston 41A (and the left door 11A connected to thispiston) is moved forward, the first one-way solenoid valve 66C isclosed, the first two-way solenoid valve 68C is opened, andpressurization of the pressurization pump 62C is started. Air passesthrough the opened first two-way solenoid valve 68C, and by the airpressure, the piston 41A is moved forward, and the left door 11A isclosed.

When the left door 11A fully closes, the air pressure rapidly increases,so that when this change is detected by the pressure sensor 64C, thepressurization pump 62C is stopped, the first two-way solenoid valve 68Cis closed, the first one-way solenoid valve 66C is opened, andcompressed air inside the left air cylinder 40A is released to theatmosphere, and the pressure inside the left air cylinder 40A decreasesto the atmospheric pressure, and the mechanism returns to the standardstate.

The same applies to the right door 11B, and an “automatic openingoperation” and an “automatic closing operation” are performed throughthe same operations in which the left air cylinder 40A corresponds tothe right air cylinder 40B, the piston 41A corresponds to the piston41B, the first one-way solenoid valve 66C corresponds to the thirdone-way solenoid valve 66E, the first two-way solenoid valve 68Ccorresponds to the third two-way solenoid valve 68E, the second two-waysolenoid valve 68D corresponds to the fourth two-way solenoid valve 68F,and the second one-way solenoid valve 66D corresponds to the fourthone-way solenoid valve 66F.

Further, an operation of the automatic calibration mechanism 80 when thecontrol unit 34 receives a command to automatically calibrate thebalance is as follows.

First, in order to inflate the air bag 81 and load the built-in weight82 onto the balance, all of the one-way solenoid valves (66C, 66D, 66E,66F, and 66G) are closed, the fifth two-way solenoid valve 68G isopened, and pressurization of the pressurization pump 62C is started.Other two-way solenoid valves (68C, 68D, 68E, and 57F) connected to thepressurization pump 62C are all closed, so that air passes through thefifth two-way solenoid valve 68G and inflates the air bag 81. By theinflation of the air bag 81, the built-in weight 82 is loaded onto thebalance. When the air bag 81 is fully inflated, the air pressure rapidlyincreases, so that when this is detected by the pressure sensor 64C, thepressurization pump 62C is stopped.

When the built-in weight 82 with a known mass is weighed and thecalibration process ends, then, in order to unload the built-in weight82 from the balance, the fifth one-way solenoid valve 66G is opened, andthe fifth two-way solenoid valve 68G is closed. Accordingly, when theair that inflated the air bag 81 passes through the fifth one-waysolenoid valve 66G and is released to the atmosphere, the air bag 81gradually deflates, and the built-in weight 82 is unloaded from thebalance. The remaining one-way solenoid valves (66C, 66D, 66E, and 66F)are opened, and the mechanism returns to the standard state.

During the calibration operation, all of the one-way solenoid valves(66C, 66D, 66E, 66F, and 66G) are closed, so that air cannot move, andthe left door 11A and the right door 11B are locked. When thecalibration operation ends, the left door 11A and the right door 11B areunlocked, and become manually openable and closable.

By locking the doors during automatic calibration, the operator isprevented from opening the left door 11A or the right door 11B bymistake without noticing automatic calibration, and causing influence oncalibration.

In the balance 101 with a windshield according to the second embodiment,the pressurization pump 62C is used as a drive source shared by the leftand right air cylinders (30A and 30B), and accordingly, the number ofcomponents can be reduced to be less than in the first embodiment, andthe cost can be reduced. A pressurization pump as a drive source thatraises and lowers a built-in weight incorporated in the balance at thetime of automatic calibration, and the pressurization pump 62C, areconfigured as a shared one, and accordingly, the number of componentscan be further reduced.

Third Embodiment

FIG. 21 is a block diagram of an opening and closing mechanism 260 for abalance 201 with a windshield according to a third embodiment. Thebalance 201 with a windshield is configured in common with the balance101 with a windshield according to the second embodiment except that anopening and closing mechanism 260 is different.

As illustrated in FIG. 21, the opening and closing mechanism 260 of thebalance 201 with a windshield includes a right air cylinder 40I to openand close the right door 11B, a left air cylinder 40H to open and closethe left door 11A, and an automatic calibration mechanism 80. A commondrive source shared by these components is apressurization/decompression pump 69.

The pressurization/decompression pump 69 can perform both pressurizationand decompression of air. The right air cylinder 401 and the left aircylinder 40H are double-acting air cylinders for thepressurization/decompression pump, and each of the air cylinders isprovided with only one port (45I/45H) at the rear side. In response topressurization of the pressurization/decompression pump 69, a piston 41Hinside the left air cylinder 40H moves forward and the left door 11Acloses, and in response to decompression of thepressurization/decompression pump 69, the piston 41H moves rearward andthe left door 11A opens. The same applies to the right air cylinder 40I.

The pressure sensor 64J monitors an air pressure inside a connected airtube to prevent the air pressure from becoming equal to or more than aset upper limit value or becoming equal to or lower than a set lowerlimit value. Outlet sides of all of the three one-way solenoid valves(66H, 66I, and 66J) are opened to the atmosphere. Each of the two-waysolenoid valves (68H, 68I, and 68J) has two connect ports, and the inletsides are connected to the pressurization/decompression pump 69, and theoutlet sides are connected to the left air cylinder 40H, the right aircylinder 40I, and the air bag 81, respectively, to control the flow andstoppage of air.

To the port 45H of the left air cylinder 40H, the first two-way solenoidvalve 68H is connected. This connection has a branch halfway, and thefirst one-way solenoid valve 66H is also connected. Similarly, to theport 45I of the right air cylinder 40I, the second two-way solenoidvalve 681 and the second one-way solenoid valve 66I are connected in thesame manner. To the air bag 81 of the automatic calibration mechanism80, the third one-way solenoid valve 66J and the third two-way solenoidvalve 68J are connected.

FIG. 22 illustrates operations of the respective components to operatethe left door 11A, the right door 11B, and the built-in weight 82 of theautomatic calibration mechanism 80.

In a standard state where the respective functions are not activated atall, the pressurization/decompression pump 69 does not operate, and allof the two-way solenoid valves (68H, 68I, and 68J) are closed, and allof the one-way solenoid valves (66H, 66I, and 66J) are opened so as tobe open to the atmosphere. In this state, both of the left door 11A andthe right door 11B can be manually opened and closed.

First, automatic opening and closing of the left door 11A are described.In the case of an “automatic opening operation” of the left door 11A,that is, when the piston 41H (and the left door 11A connected to thispiston) inside the left air cylinder 40H is moved rearward, the firstone-way solenoid valve 66H is closed, the first two-way solenoid valve68H is opened, and decompression of the pressurization/decompressionpump 69 is started. Accordingly, the pressure inside the left aircylinder 40H becomes low, and the piston 41H moves rearward and the leftdoor 11A is opened.

When the left door 11A is opened, the air pressure rapidly decreases, sothat when this decrease is detected by the pressure sensor 64J, thepressurization/decompression pump 69 is stopped, the first two-waysolenoid valve 68H is closed, and the first one-way solenoid valve 66His opened, and the mechanism returns to the standard state.

In the case of an “automatic closing operation” of the left door 11A,that is, when the piston 41H is moved forward, the first one-waysolenoid valve 66H is closed, the first two-way solenoid valve 68H isopened, and pressurization of the pressurization/decompression pump 69is started. Accordingly, the pressure inside the left air cylinder 40Hbecomes high, and the piston 41H is pushed forward by an air pressure,and the left door 11A is closed.

When the left door 11A is closed, the air pressure rapidly increases, sothat when this increase is detected by the pressure sensor 64J, thepressurization/decompression pump 69 is stopped, the first two-waysolenoid valve 68H is closed, the first one-way solenoid valve 66H isopened, and the mechanism returns to the standard state.

An “automatic opening operation” and an “automatic closing operation” ofthe right door 11B are the same as described above, and are performedthrough the same operations in which the left air cylinder 40Hcorresponds to the right air cylinder 40I, the first one-way solenoidvalve 66H corresponds to the second one-way solenoid valve 66I, and thefirst two-way solenoid valve 68H corresponds to the second two-waysolenoid valve 68I.

Further, an operation of the automatic calibration mechanism 80 to beperformed when the control unit 34 receives a command to automaticallycalibrate the balance is as follows.

First, in order to inflate the air bag 81 and load the built-in weight82 onto the balance, all of the one-way solenoid valves (66H, 66I, and66J) are closed, the third two-way solenoid valve 68J is opened, andpressurization of the pressurization/decompression pump 69 is started.Since other two-way solenoid valves (68H and 68I) connected to thepressurization/decompression pump 69 are closed, when air passes throughthe third two-way solenoid valve 68J and inflates the air bag 81, due tothe inflation of the air bag 81, the built-in weight 82 is loaded ontothe balance. When the air bag 81 is fully inflated, the air pressurerapidly increases, so that when this increase is detected by thepressure sensor 64J, the pressurization/decompression pump 69 isstopped.

When the built-in weight 82 with a known mass is weighed and thecalibration process ends, then, in order to unload the built-in weight82 from the balance, the third one-way solenoid valve 66J is opened, andthe third two-way solenoid valve 68J is closed. Accordingly, when theair that inflated the air bag 81 passes through the third one-waysolenoid valve 66J and is released to the atmosphere, the air bag 81gradually deflates, and the built-in weight 82 is unloaded from thebalance. The remaining one-way solenoid valves (66H and 66I) are opened,and the mechanism returns to the standard state.

During the calibration operation, all of the one-way solenoid valves(66H, 66I, and 66J) are closed, so that air cannot move, and the leftand right doors (11A and 11B) are locked. When the calibration operationends, the left and right doors (11A and 11B) are unlocked, and becomemanually openable and closable.

By using the pressurization/decompression pump 69 as a common drivesource for the respective components of the balance 201 with awindshield, the number of components can be reduced to be further lessthan that of the balance 101 with a windshield of the second embodimentand assembly man-hours can be reduced.

Modifications

Preferred modifications with respect to the embodiments described aboveare described. The same components as in the embodiments described aboveare provided with the same reference signs, and descriptions of theseare omitted.

FIG. 23 illustrates a modification of shapes of the cylinder box 20 andthe holder 16. A bottom surface 20 f of the cylinder box 20 which servesas an engagement surface to engage with the door 11 is inclined towardthe guide hole 20 d. A bottom surface of the flange portion 16 c whichserves as an engagement surface to engage with the cylinder box 20 isformed to be inclined at the same angle as the angle of the bottomsurface 20 f. The inclination angles of the bottom surfaces 20 f (andthe bottom surface of the flange portion 16 c) at the left and right ofthe guide hole 20 d are equal to each other, and the door 11 maintains asubstantially vertical posture. Due to the inclination of the engagementsurface toward the guide hole 20 d, the door 11 easily maintains itsposture in the vertical direction.

FIG. 24 is a modification in which, for door position detection,position sensors are used instead of the pressure sensors. At the fullyopened position and the fully closed position of the door 11,photointerrupters 92 are provided as position sensors. Eachphotointerrupter 92 has a slit 92 a, and in alignment with the positionof the slit 92 a, a projection portion 16 f is formed on the couplingportion 16 d of the holder 16. In the slit 92 a, a light emitting unitand a light receiving unit facing each other are provided, and bydetecting, by the light receiving unit, interruption of light from thelight emitting unit by the projection portion 16 f, a position of thedoor 11 is checked.

The pressurization pumps (62A and 62B) are interlocked with thephotointerrupters 92, and stop when receiving a signal indicating thatthe projection portion 16 f arrives at the position of thephotointerrupter 92. With this configuration, the door 11 can be stoppedat an accurate position.

Embodiments and modifications of the present invention have beendescribed above, and the embodiments and modifications can be combinedbased on knowledge of a person skilled in the art, and such a combinedembodiment is included in the scope of the present invention.

REFERENCE SIGNS LIST

-   1, 101, 201 Balance with windshield-   6 Weighing chamber-   10 Windshield-   11 Door-   11A Left door-   11B Right door-   14 Frame-   16 Holder-   16 c Flange portion-   17 Power chamber-   19 Engagement hole-   20 Cylinder box-   20 d Guide hole-   20 e Bottom surface-   30 Balance main body-   31 Weighing pan-   32 Floor member-   34 Control unit-   35 Control panel-   40 Air cylinder-   44, 46 Port-   60, 160, 260 Opening and closing mechanism-   62 Pressurization pump-   64A to 64C, 64J Pressure sensor-   66 One-way solenoid valve-   68 Two-way solenoid valve-   70 Attaching and detaching mechanism-   72 Engagement member-   S101 to S113 Step

The invention claimed is:
 1. An electronic balance comprising: a balancemain body including a weighing mechanism connected to a weighing pan; awindshield having a door capable of opening and closing by sliding, andconfigured to form configured to form a weighing chamber by covering theweighing pan; and an actuator configured to open and close the door,wherein the actuator includes a double-acting type air cylinder havingtwo ports serving as air intake ports; an air pump to be connected tothe two ports; two valves respectively interposed between the air pumpand the two ports and configured to make the ports communicate with andshut off from the atmosphere; and a control device configured to controlthe two valves to make the two ports communicate with the atmospherewhen the air pump is stopped.
 2. The electronic balance according toclaim 1, further comprising: a pressure sensor configured to monitor apressure of air discharged from the air pump, wherein the control deviceis configured to perform control so as to stop the air pump and make thetwo ports communicate with the atmosphere when the pressure sensordetects a rapid increase in air pressure.
 3. The electronic balanceaccording to claim 1, further comprising: a pressure sensor configuredto monitor a pressure of air discharged from the air pump, wherein thecontrol device is configured to control the two valves, in a case wherethe pressure sensor does not detect a decrease in air pressure within apredetermined time when the air pump is activated with one of the twoports being made to communicate with the atmosphere and the other oneport being made to shut off from the atmosphere, so as to reverse thecommunication with the atmosphere and communication shut-off from theatmosphere of the two ports.
 4. The electronic balance according toClaim 1, wherein a power chamber partitioned and separated from theweighing chamber is formed in the windshield, and the air pump and thetwo valves are disposed inside the power chamber.
 5. The electronicbalance according to Claim 1, wherein the door is hung and supportedfrom an upper portion, and the air cylinder is disposed above the doorand connected to a door hanging portion.
 6. The electronic balanceaccording to Claim 1, wherein the control device is configured tocontrol the valves so that communication of the two ports with theatmosphere is shut off during calibration of the balance main body. 7.The electronic balance according to Claim 1, wherein the control deviceis configured to control the valves so that communication andshutting-off between the two ports and the atmosphere are switchedaccording to a command input.